Many machines include motion-control systems that have one or more moveable components, and controls that regulate one or more aspects of the motion of the one or more moveable components. The controls of such a motion-control system may control a first operating parameter of the motion-control system to achieve a target value of a second operating parameter of the motion-control system. For example, first operating parameter, such as the steering direction of a vehicle may be controlled in accordance with a second operating parameter established by the position of a joystick.
Some motion-control systems control the first operating parameter in an open-loop manner, which entails controlling the first operating parameter in a manner estimated to achieve the target value of the second operating parameter without receiving information about the actual value of the second operating parameter. Such open-loop control strategies operate on the premise that the first operating parameter and the second operating parameter theoretically relate to one another in a known way and, accordingly, the motion-control system can theoretically control the second operating parameter in a predictable manner by controlling the first operating parameter. Unfortunately, various factors may cause the actual relationship between the first operating parameter and the second operating parameter to deviate from the theoretical relationship. Such factors may compromise the ability of a motion-control system to effectively drive the second operating parameter toward the target value with open-loop control of the first operating parameter.
U.S. Pat. No. 4,984,646 to Sano et al. (“the '646 patent”) discloses a vehicle steering system that uses a closed-loop control method. The steering system of the '646 patent includes a steering motor connected to steerable road wheels, a steering wheel mechanically decoupled from the steerable road wheels, and a controller. The controller determines a target steering angle based on the angle of the steering wheel. The controller also determines an actual steering angle based on inputs from a speedometer and a yaw rate gyroscope. The controller subtracts the actual steering angle from the target steering angle to determine a steering error. The controller multiplies the steering error by a gain factor. The steering motor controls the angle of the steerable road wheels based on the value that results from the controller multiplying the steering error by the gain factor. The controller of the '646 patent determines the gain factor as a function of the speed of the vehicle. The '646 patent discloses that, for any particular speed of the vehicle, the controller holds the gain factor constant.
Although the '646 patent discloses a steering system that uses a closed-loop control method, certain disadvantages persist. For example, using a constant gain factor for any given speed of the vehicle may compromise performance of the steering system at one or more steering error values. If the steering system uses a relatively high gain factor, the steering motor may respond undesirably vigorously to relatively low steering errors. This may make it difficult for an operator to make fine steering adjustments. It may also cause the steering system to jerk when the control error goes from zero to a positive value or vice versa. Conversely, if the steering system uses a relatively low gain factor, the steering motor may respond undesirably sluggishly to relatively large steering errors.
The motion-control system and methods of the present disclosure solve one or more of the problems set forth above.